1. Field
One or more embodiments relate to a method and apparatus for dimmable visible light communication (VLC) with error correction, and more particularly, to a technology for error correction using puncturing and scrambling in a broadcasting communication path of which intensity is adjustable.
2. Description of the Related Art
Recently, there has been wide spread use of light emitting diodes (LEDs) due to improvements in emission efficiency and reductions in the prices of LEDs.
Visible light communication (VLC) refers to a communication technology that transmits information to a receiver using visible light, such as light having a wavelength of about 400 to 700 nm, for example. In such VLC systems, information may be transmitted by flickering visible light, e.g., by an LED, at high frequencies. The frequency of the flickering may be controllable based upon a clock speed.
As only an example, a corresponding lighting device of a VLC system may be connected to a power line communication system, for example, that provides high-speed Internet through a power consent, e.g., through permission based distribution algorithms that determine efficient spectrum access, so that access to the Internet is achieved through a communication path between Internet ready devices and the light transmitting device, such as a visible path. As only an example, in such permission based distribution based algorithms, a primary user may permit secondary users access to a resource (spectrum) as long as they consent to aiding the primary user as a relay in addition to transmitting their own data. In this example, the high-speed Internet may be provided to the VLC system from a power line provided high-speed Internet so as to extend Internet access to such Internet ready devices by using the VLC system. Conventionally, such extensions have been provided by wireless local area networks (LANs). However, VLC may be more stable than the wireless LAN because information may be more easily lost through a wireless connection than VLC.
Also, VLC is typically harmless to a human body since it may use a light that, as generated or propagated, is harmless to the human body. Furthermore, obtaining frequency permissions may be necessary for wireless LANs, while such frequency permissions may not be necessary with VLC. In addition, recently the interest in VLC has increased due to limitations or the exhaustion of available radio frequency (RF) band frequencies, possibility of crossover among different types of wireless communication technologies, an increasing demand for security, and the like.
Therefore, research is being conducted for VLC by various enterprises and laboratories. In addition, there is further interest in increases in technology that may permit increases in available data transmission rates of VLC systems.
As noted above, in VLC systems information may be transmitted by flickering visible light, e.g., by an LED. The average intensity of the flickering visible light may adapt to a dimming requirement chosen by a user, which may be achieved through various transmission schemes at the modulation level. One example scheme is on-off keying (OOK), where a ratio of “ON” time to “OFF” time is adjusted in a transmission frame to meet such a dimming requirement. For example, 70% “ON” may be needed for a 70% dimming requirement. However, few VLC approaches have addressed error correction schemes that satisfy such requirements in OOK-based VLC systems. Furthermore, those schemes that do address error correction are generally based on special algebraic structures of constant weights. This results in only a limited number of dimming rates being allowed, so the adaptation to arbitrarily set dimming rates is not possible. Also, code rates are scaled with O(log N÷N) for a codeword of length N, so high code rates cannot be achieved. Basically, existing schemes exploit the constant weight property of specific codes. Since those schemes exclude the all-zero codeword, the resulting binary codes are non-linear. In addition, since the constant weight property of algebraic codes generally limits the code rates too strictly, code rates scale with O(log N÷N), which renders the coding scheme impractical except for very small N. Accordingly, existing schemes have limited code rate options as they scale with O(log N÷N) for codewords of length N. In addition, such existing schemes require separately designed and dedicated encoding/decoding methods for respective different dimming rates, with such dedicated decoding methods decreasing overall performance.